1. Field of the Invention
The present invention relates to a plasmon resonance detector using a metal structure that has plasmon resonance absorption.
2. Description of the Related Art
A fine metal body (for example, metal particulates of nanometer size) can demonstrate optical response called “localized (surface) plasmon resonance absorption” in a particular wavelength region among a wide wavelength region from the visible wavelength to the infrared wavelength, depending on the form and size of the fine metal body. Metals that demonstrate the localized plasmon resonance absorption include noble metals such as gold, silver, and platinum. However, even a metal of the same kind has a variation in the localized plasmon resonance absorption wavelength depending on its size and form. It has been attempted to apply to various optical devices such a property of the fine metal body whose absorption wavelength varies depending on differences in the size and form of the fine metal body.
A metal structure having a plurality of fine metal bodies disposed on a substrate may have the plasmon resonance absorption in the wide region from the visible region to the infrared region on the basis of a principle of the localized (surface) plasmon. When attempting to apply such a metal structure to an optical device or sensor, it is important to adjust the wavelength region of the plasmon resonance absorption.
Moreover, phenomenon that a photoelectric field enhancement phenomenon through a plasmon at the surface of the metal structure enhances infrared absorption is found out (for example, see Applied Physics A, vol. 29, pp. 71-75 (1982)). However, these mechanisms have not been clarified yet and a method for quantitative measurement of the enhanced absorption or the like has not been established. Therefore, when the metal structure having a plasmon resonance frequency in a desired infrared region can be produced, an optical device or measurement system using the above-mentioned phenomenon will be constructed.
The wavelength region of the plasmon resonance absorption that the above-mentioned metal structure has is influenced by the “elongated form of the fine metal body disposed on the substrate (aspect ratio when the fine metal body is rod-like).” In other words, disposition of the elongated fine metal body (with a higher aspect ratio) on the substrate shifts the wavelength region of the plasmon resonance absorption to a longer wavelength side, while disposition of the short fine metal (with a lower aspect ratio) on the substrate shifts the wavelength region of the plasmon resonance absorption to a shorter wavelength side.
On the other hand, a technique by which a plurality of rod-like nano metal (gold: Au) bodies are chemically bonded and connected has been known (for example, see J. Phys. Chem. B, 108, 13066 (2004) and JACS, 125, 13915 (2003)). These nano metal bodies are just bonded through a chemical substance that is not a metal, and strictly speaking, these nano metal bodies have a structure of single metal bodies in which the nano metal bodies are not directly connected to each other. The nano metal bodies can therefore obtain the plasmon resonance absorption on the side of the longer wavelength.
By the way, when optical devices such as photodetectors and devices for measuring absorbance are produced using a nano metal body as mentioned above, it is necessary to use a micro FT-IR measuring device or the like for measuring existence and strength of the plasmon resonance absorption. In addition, a device for optical analysis is needed even when it is desired to use the optical device as a plasmon resonance sensor for which the nano metal body is used. This causes a problem of increase in size of the optical device.
The present invention has been made to solve the above mentioned problem. An object of the present invention is to provide a plasmon resonance detector for which a metal structure having plasmon resonance absorption is used, and that can detect plasmon resonance with a simple structure allowing miniaturization of the detector.